Chemistry Module 1- Basic Revision Notes 1.1a Atomic Structure 1.1.1 All matter is composed of atoms – very small particles. The atoms are composed of 3 sub-atomic particles called:(i) Protons – located in the centre of the atom (ii) Neutrons – located in the centre of the atom (iii) Electrons – orbiting around the nucleus The nucleus is the concentration of mass at its centre i.e. protons and neutrons. The electrons orbit the nucleus Diagram 1: Shows the Helium atom Electron Neutron { Nucleus Proton 1.1.2 All the elements are listed in the periodic table in the form: Mass number Atomic number A X Element symbol Z Name Element name A – Mass number, the total number of protons and neutrons e.g. 12C Carbon has 6 protons and 6 neutrons Z – Atomic number, the total number of protons which is equal to the number of electrons. www.astarexams.com 1 Copyright © 2008-2009 Celtic Educational Services Ltd. All Rights Reserved. e.g. 6C Carbon has 6 protons = 6 electrons (for a neutral atom) The electronic structure of atoms can be written in two ways. 1. Electronic notation e.g. 3Li would be 2.1 11Na would be 2.8.1 19K would be 2.8.8.1 NB The first orbit, or shell, can only hold 2 electrons. The second orbit can hold a maximum of 8 electrons. The third shell will also hold up to 8 electrons. 2. Electron shell diagrams e.g. X X X X X X X lithium(Li): 2.1 X X X X X X X X X Sodium(Na): 2.8.1 X X X X X X X X www.astarexams.com X X X X X X X Potassium(K): 2.8.8.1 X X 2 Copyright © 2008-2009 Celtic Educational Services Ltd. All Rights Reserved. 1.1b Elements and the Periodic Table 1.1.3 Elements (H, He, Li, Be,…..) are the basic building blocks of all matter, and cannot be broken down into simpler parts by chemical means. 1.1.4 There is a clear relationship between an elements electronic structure and its position in the periodic table. P E r i o d 1 2 3 4 The Periodic Table (First 4 rows only) Group No I 1H 1 3Li 2.1 11Na 2.8.1 19K 2.8.8.1 II 4Be III 5B IV V 6C 7N VI 8O 2.2 2.3 2.4 2.5 2.6 12Mg 13Al 14Si 15P 16S 2.8.2 2.8.3 2.8.4 2.8.5 2.8.6 2oCa 2.8.8.2 (The transition metals have been left out) VII 9F 2.7 17Cl 2.8.7 VIII 2He 2 10Ne 2.8 18Ar 2.8.8 By looking at the above table, you can see that the last number in the electronic structure, corresponds with the group number e.g. 2.1 = group I 2.5 = group V Also the electronic structure gives the period number e.g. 2.1 = period 2 2.8.1 = period 3 Plus the total number of electrons gives the atomic number. e.g. 2.1 = atomic number 3 2.5 = atomic number 7 Here are some more examples from the periodic table above:Element 3Li 15P 13Al 18Ar 20Ca www.astarexams.com Electronic Structure 2.1 2.8.5 2.8.3 2.8.8 2.8.8.2 Group Number I V III VIII II Period Number 2 3 3 3 4 3 Copyright © 2008-2009 Celtic Educational Services Ltd. All Rights Reserved. 1.1.5 Mendeléev’s Discoveries He observed repeating patterns in the properties of elements, when arranged in order of increasing relative atomic mass. But he was cleaver and left gaps for elements that had not yet been found. This allowed him to predict the properties of the unknown elements. 1.1.6 Metals and Non-metals Properties of Metals Good conductor of electricity Good conductor of heat High melting points High boiling points Shiny (Luster) Some are magnetic Sonorous (Ringing sound) Ductile (Drawn into a wire) Malleable (Easily hammered into shape) Properties of Non-Metals Good electrical insulator Good heat insulator Low melting points Low boiling points Dull If you know the above properties then telling the difference between metals and nonmetals should be relatively easy. But there are exceptions to look out for:(i) Carbon (graphite) - good conductor of electricity (ii) Mercury -liquid metal (i.e. low melting point) www.astarexams.com 4 Copyright © 2008-2009 Celtic Educational Services Ltd. All Rights Reserved. 1.1.7-8 Properties and Reactions of Group1 – the alkali metals Group I metal Lithium Sodium Potassium Rubidium Caesium Francium Atomic Number 3 11 19 37 55 87 Density Melting Point (g cm-3) (oC) 0.53 180 0.97 98 0.89 63 1.50 39 1.93 28 2.40 27 Boiling Point (oC) 1360 900 777 705 678 677 These metals are the most chemically reactive group of metals and increase in reactivity down the group, they also, are known as soft metals(i.e. can be cut easily by a knife) are low in density(i.e. they even float on water) are stored under paraffin (oil) due to their high reactivity with water react quickly with oxygen (in the air)and tarnish are shiny when newly cut open Reactions of Group I (a) Alkali metal with water General Equation: Metal + Water e.g. 2Na (s) + 2H2O (l) Metal Hydroxide + Hydrogen gas 2NaOH (aq) + H2 (g) (‘pop’ test for hydrogen!) (Solution made has a high pH) The reaction type and balancing stays the same for all Group I metals i.e. 2Fr (s) + 2H2O (l) 2FrOH (aq) + H2 (g) (b) Alkali metal with oxygen General equation: Metal + Oxygen Metal Oxide e.g. 4Na (s) + O2 (g) 2Na2O (s) (Also known as Oxidation) The reaction type and balancing stays the same for all Group I metals i.e. 4Fr (s) + O2 (g) www.astarexams.com 2Fr2O (s) 5 Copyright © 2008-2009 Celtic Educational Services Ltd. All Rights Reserved. (c) Alkali metal with halogen General Equation: Metal + Halogen e.g. 2Na (s) + Cl2 (g) 2NaCl (s) Salt The reaction type and balancing stays the same for all Group I metals i.e. 2Fr (s) + Cl2 (g) 2FrCl (s) (Remember that the Halogens are diatomic! i.e. Cl2, Br2) The latter equations are very common in GCSE examinations. Also, you should be prepared to write the word equations. (d) Diatomic molecules These molecules are very common in GCSE symbol equations. Many of them tend to be gases. The following list of diatomic molecules should be known and learned:- H2, N2, O2, F2, Cl2, Br2, I2, and At2. Remember that Bromine is a liquid at room temperature, whilst Iodine and Astatine are solids at room temperature. The above diatomic molecules have only one element type. But there are ones that are not made up of the same elements e.g. CO – carbon monoxide, NO – nitrogen oxide. www.astarexams.com 6 Copyright © 2008-2009 Celtic Educational Services Ltd. All Rights Reserved. Properties and Reactions of Group VII – the halogens Properties Halogen molecule Fluorine Chlorine Bromine Iodine Astidine Formula F2 Cl2 Br2 I2 At2 Colour Air Yellow Yellow/Green Red Black Black Water Yellow/Green Orange Brown Unknown State Gas Gas Liquid Solid Solid Melting Point (oC) –188 –34 58 183 302 The halogens are the most reactive non-metals it’s no wonder that the chemistry with Group I is so important and extensive. The Halogens: become less reactive going down the group the vapours of the halogens are (i) Smelly (ii) Coloured (iii) Diatomic (iv) Poisonous www.astarexams.com 7 Copyright © 2008-2009 Celtic Educational Services Ltd. All Rights Reserved. Reactions of Group VII (a) The halogens with water chlorine + water Cl2 (g) + H2O (l) hydrochloric acid + chloric(I) acid (Bleach) HCl (aq) + HOCl (aq) (b) Displacement reactions The word and symbol equations together with the colours produced needs to be learned well. Halide Salt Solutions Halogen Solutions Chlorine solution Bromine solution Iodine solution Potassium Chloride No Reaction (iii) (v) Potassium Bromide (i) No Reaction (vi) (i) Cl2 (aq) + 2KBr (aq) Green Solution 2KCl (aq) + Br2 (aq) Orange Solution (ii) Cl2 (aq) + 2KI (aq) Green Solution 2KCl (aq) + I2 (aq) Brown Solution (iii) Br2 (aq) + KCl (aq) Orange Solution No displacement Orange Solution (iv) Br2 (aq) + KI (aq) Orange Solution 2KBr (aq) + I2 (aq) Brown Solution (v) I2 (aq) + KCl (aq) Brown Solution No displacement Brown Solution (vi) I2 (aq) + KBr (aq) Brown Solution No displacement Brown Solution Potassium Iodide (ii) (iv) No Reaction NB The halide salt solutions are all colourless. www.astarexams.com 8 Copyright © 2008-2009 Celtic Educational Services Ltd. All Rights Reserved.